feat: 初始化 Nest 服务骨架与多平台 Chat SSE 网关

- 新增 NestJS + Fastify 入口、配置模块与 Swagger 集成
- 划分 client-app / admin-app 与 shared-domain ai-gateway
- 实现统一 SSE Chat 接口，支持千问、DeepSeek、火山引擎非流式上游与网关分片输出
- 补充项目方案与 JWT 最小实现文档

Made-with: Cursor

src/apps/client-app/chat/chat.module.ts

@@ -0,0 +1,13 @@
+import { Module } from '@nestjs/common';
+import { ChatController } from './controllers/chat.controller';
+import { ProviderRouterService } from '@shared/ai-gateway/router/provider-router.service';
+import { QwenProvider } from '@shared/ai-gateway/providers/qwen.provider';
+import { DeepseekProvider } from '@shared/ai-gateway/providers/deepseek.provider';
+import { VolcProvider } from '@shared/ai-gateway/providers/volc.provider';
+
+@Module({
+  controllers: [ChatController],
+  providers: [ProviderRouterService, QwenProvider, DeepseekProvider, VolcProvider],
+})
+export class ChatModule {}
+